200 Cytologia 23 Cytology of Oxalidaceae P. M. Mathew Botany Department, University College, Trivandrum, India Received January 24, 1958 Introduction The family Oxalidaceae consists of seven genera (Rendle 1952) and about 900 species, mostly pantropical, the greater number of which being dis tributed in the warmer parts of the world. Of the seven genera, Oxalis with about 800 species, which has one centre of distribution in South Africa and another in South America, forms the most conspicuous genus. The family is not well represented in India. Hooker (1875) lists only 15 species belonging to four genera as occurring in India. Gamble (1915) reports 9 species in three genera, Oxalis (1 species), Biophyturn (6 species) and Averrhoa (2 species), in the former Presidency of Madras. Rama Rao (1914) has recorded 6 species in three genera as occurring in Travancore. A considerable amount of work has been done in the past on the aytology of the family, especially on the important genus, Oxalis. As early cs 1927 Heitz listed the chromosome numbers of 26 species of Oxalis. Later investigators like Matsuura and Suto (1935), Kostoff et al (1935), Yamashita (1935), Wulff (1937) and Rutland (1941) have reported the cytology of about a dozen species of Oxalis. Quite recently Marks (1956) has studied the cytology of 24 species of Oxalis, of which 16 were South African and the rest South American. Krishnaswamy and Raman (1949) counted the chromosome number of one species of Averrhoa. The study reported here concerns five species of Oxalis namely O. pubescens, O. corniculata, O. pes-caprae, O. violacea and O. tetraphylla, two species of Averrhoa namely A. carambola and A. bilimbi and one species of Biophytum namely B. sensitivum. Materials and methods The materials for this study were collected from different places in South India. Oxalis pubescens, O, pes-caprae and O. tetraphylla were collected in September 1954 from Kodaikanal, where they are grown as garden plants. O. violacea was collected from Peermade. All the above mentioned species of Oxalis were found to grow well at higher altitudes. Other species like O. corniculata, Biophytum sensitivum, Averrhoa corambola and A. bilimbi were available locally in Trivandrum. In all these materials the chromosome counts were made from pollen 1958 Cytology of Oxalidaceae 201 mother cells during meiosis. For this purpose flower buds were usually collected from plants growing in their natural condition and were fixed in Carnoy's fluid (absolute alcohol and glacial acetic acid in the ratio 3:1). Use of a trace of iron acetate in the fixative was found to be helpful in some cases in getting well stained preparations, but in the case of Oxalis this Text-figs. 1-8. Explanatory diagrams of Figs. 1-8 in Plate V. All Figs. •~1125. 1. Oxalis pubescens, n=24. 2, O. corniculata, n=24. 3, O. pes-caprae, n=14. 4, O. tetraphylla, n=28. 5, O. violacea, n=14. 6, Averrhoa bilimbi, n=11. 7, A. carambola, n=11. 8, Biophytum sensitivum, n=9. did not produce any improvement on account of the tendency of the cytoplasm to absorb the stain. Fixed materials kept under low temperature in a re frigerator for at least a week produced sufficiently good results. Slides were prepared according to simple acetocarmine technique. Photomicrographs were 202 P. M. Mathew Cytologia 23 taken usually from fresh smears. Explanatory diagrams were drawn on enlarged photographic prints taken on smooth white matt paper which were reduced to desired size in reproduction. Observations Oxalis Linn. This is a tropical and subtropical genus consisting of over 800 species. In a monograph of the genus, Knuth (1930) describes them in 37 sections. Several species and varieties are grown as ornamental plants because of their brilliant yellow or purple flowers and beautiful foliage. The chromosome numbers of about 62 species have been reported by earlier investigators (listed elsewhere). Cytology of five species have been reported here, of which Oxalis corniculata is the only species indigenous to South India. All the others are introduced plants. O. pubescens H. B. and K. There is no previous cytological report on this species. During meiosis 24 bivalents were clearly observed in pollen mother cells at diakinesis (Text Fig. 1 and P1. V, Fig. 1) O. corniculata L. Two chromosome numbers have been reported in this species by previous workers. While Rutland's report (1941) shows the number as 2n=24, Marks (1956) reported it as 2n=48. Result obtained from the present study agrees with that of Marks. During meiosis 24 bivalents were clearly counted from pollen mother cells at first metaphase (Text-Fig. 2 and P1. V, Fig. 2). Bivalents at this stage showed a clumping tendency. O. pes-caprae L. The chromosome number of this species has been reported by Marks (1956) as 2n=28. Present study also showed the same number. The number of bivalents observed during meiosis was 14 (Text-Fig. 3 and Pl. V, Fig. 3) O. violacea Linn. The cytology of this species is studied for the first time. The chromo some number was found to be the same as that in O. pes-caprae. This was found to be a comparatively difficult cytological material owing to the tendency of the cytoplasm to absorb and retain the stain. Meiosis was quite normal with regular anaphase separation which resulted in the clear disposi tion of 14 chromosomes each on either side of the cell. The metaphase of the second division with 14 chromosomes each in two groups is shown in Text-Fig. 5 and P1. V, Fig. 5. O. tetraphylla Cav. Of all the species of Oxalis studied during the present investigation this species showed the highest chromosome count. The number of bivalents Cytologia, 1958 Plate V P. M. Mathew: Cytology of Oxalidaceae 204 P. M. Mathew Cytologia 22 observed at metaphase I in pollen mother cells was clearly 28 (Text-Fig. 4 and P1. V, Fig. 4). Bivalents in this stage were very much condensed and they were smaller than those in the other species of Oxalis. Biophytum De Cand. This is a tropical genus with about 50 species. It is represented in India by 8 species (Hooker 1875), of which the cytology of only one is reported here. No previous cytological report on this genus is available. B. sensitivum DC. Prodr. Meiosis was studied from materials collected from two localities and the haploid chromosome number was found to be 9 in both. Bivalents at metaphase I are appreciably condensed and they take very good stain (Text Fig. 8 and P1. V. Fig. 8). They were comparatively smaller in size. Averrhoa Linn. This is a tropical arborescent genus with only two species, A. bilimbi and A. carambola. These are cultivated for their fruit which tastes like goosberry. A. bilimbi Linn. There is no previous report on the chromosome number of this species. The number of bivalents counted from pollen mother cells at metaphase I was clearly 11 (Text-Fig. 6 and P1. V, Fig. 6). Meiosis was normal with regular anaphase separation. A. carambola Linn. The chromosome number in this species has been reported by Krishnas wamy and Raman (1949) as 2n=24. But the present study does not agree with their findings. The number of bivalents observed in several pollen mother cells was very clealy 11 (Text-Fig. 7 and P1. V, Fig. 7). The division was normal and four pollen grains of equal size were formed from each mother cell. In the accompanying list is given the chromosome numbers so far known in the family Oxalidaceae. Present study 1958 Cytology of Oxalidaceae 205 Previous reports 206 P. M. Mathew Cytologia 23 Discussion Basic chromosome number and relationship of Oxalidaceae From the chromosome determinations so far made on the family, as seen from the list above, it is obvious that Oxalis is a multibasic genus with fairly wide range of basic chromosome numbers. O. bupleurifolia is reported to have 2n=10 (Heitz 1927 and Marks 1956), and as this is the lowest diploid number so far known in the genus, 5 may be taken as the lowest basic chromosome number in Oxalis. Some of the other pre viously investigated species like O. eriolepsis Wedd. (2n=20), O. versicolor L. (2n=30), O. ciliaris Jacq. (2n=40) etc. show different grades of polyploidy on the basic number 5. However, no species of Oxalis, which can be brought under the group with 5 as basic number, has been observed during the present study of the genus. South African and South American species like O. cuneata Jacq., O. dispar Brown, O. rosea Jacq. and O. chrysantha Jacq., all showed 2n=12 (Marks 1956), and from these counts it is clear that 6 is the next higher basic number in Oxalis. Species like O. stricter L. with 2n=24 (Wulff 1937), and O. corniculata L. and O. pubescens H. B. and K., both with n=24, evidently are polyploid species on this number. Of the 62 species of Oxalis previously studied, the vast majority of them showed chromosome numbers in multiples of 7, and in the present study also three species out of five, such as O. violacea (n=14), O. pes-caprae (n=14) and O. tetraphylla (n=28), have chromosome numbers agreeing with the basic number 7. This would mean that 7 is the predominant basic number in Oxalis, and on account of this Marks (1956) has even suggested that 7 is probably the archaic basic number for the genus, all others being 1958 Cytology of Oxalidaceae 207 derived from it by fragmentation or fusion of chromosomes during the course of evolution. Species like O. valdiviensis , possessing 2n=18 (War burg, 1938 and Marks 1956), and O.